High-performance display devices, such as liquid crystal displays (LCDs) and plasma displays, are commonly used in various electronics, such as cell phones, laptops, electronic tablets, televisions, and computer monitors. Currently marketed display devices can employ one or more high-precision glass sheets, for example, as substrates for electronic circuit components, or as color filters, to name a few applications. The leading technology for making such high-quality glass substrates is the fusion draw process, developed by Corning Incorporated, and described, e.g., in U.S. Pat. Nos. 3,338,696 and 3,682,609, which are incorporated herein by reference in their entireties; however, embodiments described herein are applicable to any forming process including slot draw, redraw, float, and the like.
For each of these applications, a glass sheet is typically cut to size, and then resulting sharp edges of the glass sheet are beveled by grinding and/or polishing. Cutting, edge machining, grinding and other processing steps can introduce flaws, such as chips or cracks, at surfaces and edges of the glass sheet. These flaws can serve as fracture sources and thereby reduce the strength of the sheets, particularly if the glass is flexed such that the flaw experiences tensile stress. Non-flexible display devices experience some flexing, thus the existence of these flaws may be of concern. Flexible display devices by their very nature, may produce significant stress in the display substrate(s), either during the manufacturing process or in use. Thus, flaws that might be present in the glass may experience stresses sufficiently great that the glass will crack. Since typical display manufacturing involves cutting the glass to form individual displays, and cutting is known to create multiple flaws in the glass along the cut edge, glass substrate-based flexible display devices may have a higher probability of fracture.
Attempts to mitigate flaws at the edges of glass sheets have included laser cutting, grinding, polishing and so forth, all in the attempt to remove or minimize the flaws that are created when the glass sheet is cut to size. However, many of these approaches are unsatisfactory either because the technique is incapable of removing flaws down to the size needed for the expected stresses or because the technique is difficult to apply such thin glass sheets (less than about 0.4 mm thick). Acid etching of glass edges may be used, but this may degrade the display device disposed on the substrate. Thus, flaws will continue to be formed in glass sheets, in particular at the edges of the sheet, and there is a need in the industry to accurately test edge strength of such glass sheets and panels or laminate structures using such glass sheets.